日本

Challenges to accurate and reliable data in renewable energy

2019-11-25 | Renewable energy

While the cost to implement and maintain photovoltaic (PV) has dropped substantially in recent years, the cost is not trivial. PV and microgrid design companies must constantly prove the viability and ROI of these systems. The way they do this is through data.

These companies look at data in different ways:

  • How good is it?
  • How do we manage it?
  • How do we use it?
Workers and industrial solar panels

These may seem like simple, straightforward questions, but with PV and microgrid designs, there are a lot of moving parts. A microgrid combines rooftop solar, wind, battery, and diesel/natural gas generators to form a shared supply for local demand. So, the question is: how do you gather good data, manage it with confidence, and use it to ensure the reliable delivery of electricity?

1. Data integrity

You start with trustworthy data. Trustworthy means accurate and secure. Data collected during the commissioning and testing of a new system, and throughout the lifetime of the system, will likely rest with a solar or generation technician. Their tool of choice to gather accurate test data is a digital multimeter. Data can be stored within the digital multimeter, stored locally (on a computer) and/or stored remotely via a cloud database.

Note that a digital multimeter is only as good as it is accurate. Fluke recommends you calibrate your digital multimeter on an annual basis, if not more often.

  • Field calibrators like Fluke’s 725 Multifunction Calibrator, enable digital multimeters to accurately test distributed energy resource (DER) production, such as solar PV array voltage and current.
  • Calibrators must be four or more times better than as required by the test specifications of the workload.

Fluke Connect lets you upload data directly to a cloud-based server and share with other techs in the field or back at the office.

2. Data management

Equipment performance should be logged in a computerized maintenance management software like Fluke’s eMaint to minimize downtime and extend life.

Data should be measured at regular intervals to establish a baseline. Looking at deviations from the baseline allows issues to be effectively diagnosed. You should have a Supervisory Control and Data Acquisition (SCADA) system in place to monitor your site’s DERs, energy storage and demand.

Since microgrids often have many owners, knowing how to divide the bill and the revenue is vital. For instance, in a community solar system there may be over 500 individual owners of a system. Customer management software enables individual subscribers to track their share of the production.

3. Using the data - distributed energy resource optimization

Have sensors that output data to a SCADA like Fluke Connect where you can see trendlines to easily pinpoint a ground fault, hot spot or other issue. When current is read on the EGC or a module temperature spikes, an alarm will sound alerting you to the issue. With Fluke Mobile®, this data can be read instantly on a smart phone, saving you time and money.

A good example of why DER optimization is important

Your inverter won’t start until noon and you’re unsure why. Fluke Connect shows the voltage readings from a string inverter with cell temperatures (see below). What could be determined?

String voltage trendline during the day in voltage and temperature over time

Until about 1200 hours, the string voltage is above 600V, the inverter’s maximum input voltage. This shows that the inverter is off. The only time the string voltage is below 600V is between 1200 to 1630 hours.

The cell temperature readings show that with the low temperatures in the morning and evening, the voltage increases, and the string exceeds the inverter’s maximum input voltage. But at 1200 hours, the temperature increases enough to decrease the string’s voltage to below 600V; the inverter starts and runs until about 1630 hours when the temperature again falls, increasing string voltage to above 600V.

Ultimately, cold temperatures were not considered when the system was designed. But with the new data you have, you know you have too many modules on your string and can accommodate for that.

About the expert

Michael Ginsberg is a solar expert, trainer for the U.S. Department of State, author and Doctor of Engineering Science candidate at Columbia University. He is also chief executive officer of Mastering Green, where he has trained nearly a thousand technicians worldwide in solar PV installation, maintenance, and operation.

Related resources